Marine Batteries: Best Products for Your Boat

Powering a boat using marine batteries might seem complicated, but if you start by understanding your needs, choosing the right battery will be less intimidating.

Focusing on three considerations—function, type, and size — will make finding the best marine battery easy. 

When buying a boat, it pays to know what’s inside, whether a marine battery needs replacing or the electrics will be upgraded.

Though dual-purpose batteries can work on smaller vessels, a marine battery usually serves one of two purposes: as a starter battery or as a house battery bank.

Deep-cycle batteries (sometimes called house batteries) are designed to be drained and recharged often. They power appliances and accessories, from chartplotters to air conditioners and fridges.

Meanwhile, starting batteries must deliver a great burst of energy to start an engine and crank it to life.

Batteries in boats that sit still in storage or in the off-season must also be maintained.

Whether maintaining a well-used boat, upgrading a house bank or equipping a brand-new vessel, choosing the right power units is important.

The size of the battery is measured in amp hours (Ah) and indicates time relative to usage. Size IS NOT represented by the Group number on a battery, which expresses the battery’s physical size.

Types of Marine Batteries by Purpose

There are two purposes or types of batteries for boats.

Starting Batteries

Starter batteries, also known as cranking batteries, are designed to deliver a large amount of power in a short burst to crank an engine into life.

Cranking batteries produce high current output quickly, referred to as cranking amps (CA) in warmer conditions like Florida or cold cranking amps (CCA) used to determine reliability in colder climates.

Marine cranking amps (MCA) measure the amount of amps a battery can continuously output for 30 seconds at 32℉ or 0℃ for boating.

For simple boating purposes and in situations where the battery is removed from the boat, one can get away with cheaper batteries. Not so when the battery stays in the boat all year round.

Some competitively priced batteries can be bought at Westmarine. Westmarine batteries are made in the US by Easy Penn.

($119 at Westmarine.com)

Lithium-ion batteries usually don’t have as much cranking amperage and, therefore, don’t make good starter batteries unless needed in a pinch. Therefore, lead acid batteries are usually best value with more expensive AGMs able to serve, too.

While a 650 MCA battery can crank most 150 hp engines to life, there’s a more precise way to determine the minimum needed.

Starter batteries are not meant for sustained power use and should not be used for trolling motors or other electronics for extended periods.

• Type: Flooded Lead Acid, AGM (Absorbed Glass Mat)
• Use: Engine starting
• Characteristic: High burst of power, not for deep discharge

Deep Cycle Batteries

Deep-cycle batteries are built to provide a steady amount of current over a long period, making them ideal for running trolling motors, lights, and other electronics.

A deep-cycle battery is not a starter battery intended to crank an engine into life. It’s sometimes referred to as a “house battery” for powering appliances like the fridge when disconnected from shore power.

($750 at Westmarine.com)

Thicker plates for storing energy allow them to be discharged and recharged many times.

As noted above, lead-acid batteries shouldn’t sink below 50% charge, as they will be damaged by a process called sulfation. If this happens, it can be remedied or desulfated if it’s a soft sulfation and done soon after.

Lead-acid batteries are easily the cheapest and, in many situations, a good enough solution for most boats. Just keep them charged (over 50%) with either a charge controller and disconnect them when not in use.

• Type: Flooded Lead Acid, AGM, Gel, Lithium-ion
• Use: Powering appliances and trolling motors
• Characteristic: Sustained energy delivery, withstands frequent discharging, can be maintained with solar and wind power generation

Dual-Purpose Batteries

Dual-purpose batteries offer the benefits of both starting and deep-cycle batteries. They can start an engine and power onboard accessories, though they may not perform each function as well as a dedicated battery would.

A dual-purpose battery can be a practical choice for boaters with limited space or a simpler setup. A jon boat or with lights and stereo, for example, or a bass boat to power a small fridge.

• Type: Lead Acid, AGM
• Use: Starting and moderate deep cycle use
• Characteristic: Versatile, space-saving

Standard Flooded Lead Acid vs. AGM vs. Lithium-Ion

There are a lot of choices but knowing what the needs are leads to the next question: how much power is needed and how many batteries? Batteries are measured in amperage values called amp hours (AH).

Battery monitors can help determine power needs onboard a boat and will give a good idea what kind and size battery is needed.

An example of a mini-fridge with a Lead Acid or AGM battery can go as follows:

A 65 watt fridge on an 80Ah battery (50% usable: 40Ah) might REALISTICALLY run 10-12 hours.

At 12 volts, 65 watt fridge uses about 2.7 amps/hour, which divides the size of the power (40 / 2.7 = 14.8  hours of use).

On the other hand, an 80Ah lithium battery can be drained completely and, therefore, can provide 20-24 hours (100% of its 80 amp hours).

Therefore, on paper, without opening the fridge or power surges, a 80Ah lithium battery presents this: 80 / 2.7 = 29.63 hours.

Throw in some wind or solar regeneration and multi-day, off-grid boating with electricity is possible.

Using this above example, we can better understand the advantages of the more expensive Lithium batteries, but there’s more to consider.

Here’s a breakdown of the 4 types:

• Flooded lead acid
• Gel
• AGM, and
• Lithium-Ion

Flooded Lead Acid Batteries

Flooded lead acid batteries are cheap solutions for casual maritime use. They require some maintenance and the effective available use is only about ⅓. In fact, they should never be discharged under 50%, a level known as the battery floor.

There is quite a bit of maintenance involved to prolong the life of flooded lead acid batteries and they have a higher monthly discharge rate, meaning they need to be periodically charged during times of disuse.

To get 200 amp hours out of a flooded lead acid battery, a 600AH bank is needed.

AGM Batteries

AGM stands for absorbent glass mat, which is just a sealed housing. This sealed VRLA battery is popular for its advantages over standard flooded lead acid batteries, including lower maintenance, lighter weight, faster charge time, and slower discharge time. They deal with colder temperatures better, too.

On account of the valve regulated technology, they lose less charge through effusion (gas escaping). In the 1980s, the US military began using AGM batteries for their nuclear sub-fleet.

Virtually any kind of battery tender can also charge AGM batteries. Some chargers will have a switch to change from a standard flooded battery to a gel or an AGM kind, but AGM is as compatible as lithium-ion batteries with cheaper chargers.

Gel Batteries

Even though they are twice the price, gel batteries have a lot of advantages. The electrolyte catalysts are sealed inside the battery house in gel form, meaning they won’t spill. Gel batteries are also VRLA batteries that prevent gas from escaping during discharge.

They are great for boats that spend a lot of time not in use. But they require a specific, well-working charging system. These are, essentially, approved upon versions of the AGM.

Lithium-ion Batteries

Lithium-iron phosphate type (LIFEP04) is the most expensive battery for a boat’s power bank. It is the same type in your smartphone, and can similarly, drain down to 0%.

They are faster-charging batteries and lighter than the others.

They have the best cycle life, meaning they offer between 3000 and 5000 lifecycles, and they charge crazy fast. They don’t require maintenance and don’t discharge any gas when charging.

Technical Specifications

Choosing how much to pay should consider marine battery design and technical specifications, such as capacity and cranking amps. These play a pivotal role in the battery’s performance and reliability in marine environments.

Battery Capacity

Battery capacity is measured in ampere-hours (Ah) and indicates the energy stored in the battery. The higher the capacity, the longer the battery lasts before recharging. For example, a Lithium battery rated at 100Ah can deliver 5 amps for 20 hours. Lead acid should only discharge to 50% and therefore, half that time.

• Rated Capacity: Measured in Ah (ampere-hours)

Cranking Amps and MCA

Marine Cranking Amps (MCA) refers to the current a battery can provide at 32°F (0°C) for 30 seconds while maintaining a voltage above 7.2 volts. It’s typically higher than the CCA because the temperature is less extreme.

• Marine Cranking Amps (MCA): Current measured in amperes for 30 seconds at 32°F (0°C)

Cold Cranking Amps (CCA)

Cold Cranking Amps (CCA) is a key specification and it denotes the number of amps a battery can deliver at 0°F (-18°C) for 30 seconds while maintaining a voltage above 7.2 volts. It’s crucial for starting engines in cold climates.

• Cold Cranking Amps (CCA): Current measured in amperes for 30 seconds at 0°F (-18°C)

Design and Build Quality

When selecting marine batteries, we consider the design and build quality paramount as these factors directly influence battery lifespan and the construction materials determine the overall durability and performance under marine conditions.

Battery Lifespan

Marine batteries feature thick lead plates essential in withstanding deep discharge cycles, which are characteristic of marine applications.

Their longevity is often expressed in cycle life, which is the number of complete charge and discharge cycles a battery can perform before its capacity falls to a certain percentage of the original.

• Cycle Life Indicators:
  • Deep cycle batteries: >1200 cycles at 50% depth of discharge (DOD)
  • Starter batteries: fewer cycles due to design for short, high current bursts

Generally, more expensive batteries tend to offer a greater cycle life due to superior build quality.

Battery lifespan is affected by usage patterns and maintenance. Proper care can prevent corrosion, one of the main causes of reduced lifespan in marine batteries.

Construction Material

Our marine batteries are constructed mainly with lead plates. The thickness and quality of these plates play a critical role in combating the harsh maritime environment, which can accelerate corrosion.

• Materials Used:
  • Plates: Heavy-duty, thick lead plates
  • External Casing: Durable, corrosion-resistant material

The reserve capacity (RC) of a battery is measured in minutes. RC is the time a 12V battery runs before dropping to 10.5 volts. Divide Ah by 25 then multiply by 60 to find the RC of a battery.

(Westmarine Dual-Use Marine Battery 80Ah, $161)

A higher reserve capacity means the battery can run longer before recharging, enhancing its usability in marine environments where port charging facilities may be sporadic.

Price and Value

When we consider the price of a marine battery, we also need to evaluate its value over time. While initial costs are important, the eventual expense includes replacement and maintenance. Here’s a quick comparison:

• AGM (Absorbed Glass Mat): Higher upfront cost but less maintenance and a longer lifespan.
• Flooded Batteries: Lower cost but require more upkeep and may need more frequent replacement.
• Lithium: Higher upfront cost with faster recharging, longer life-cycle and can discharger below 50% without damage.

Battery Maintenance and Long-Term Use

The long-term use of a marine battery largely depends on our commitment to routine maintenance. Boat maintenance should always include battery care to prevent issues and extend its life. Here’s how different battery types stack up:

• Flooded Batteries: Need regular checking for water levels and terminal cleaning.
• AGM Batteries: Virtually maintenance-free but must be stored and charged properly.
• Lithium Iron Phosphate Batteries: Minimal maintenance with a state-of-the-art battery management system to monitor state of charge.

Brand Overview and Market Trends

Notable Manufacturers

The marine battery market comprises several key players, each with their specialized products.

For example, Relion Batteries has become well-known for their lithium iron phosphate (LiFePO4) batteries, which offer longevity and reliability for marine applications. Another prominent name is Odyssey Batteries, well-regarded for their robust AGM (Absorbent Glass Mat) marine batteries.

Alongside them, some other notable manufacturers focus specifically on marine starting batteries and marine dual-purpose batteries. These include trolling motor batteries for electric trolling motors and house batteries for supplying power to onboard accessories. The market segments can be defined as follows:

• Trolling Motor Batteries: Dedicated batteries for electric trolling motors.
• House Batteries: Designed to power onboard appliances and electronics, which are getting drained and recharged again.
• Marine Starting Batteries: Optimized for high bursts of starting current.
• Marine Dual-Purpose Batteries: Combine starting and deep cycling features.

Consumer Preferences

We observe a consumer shift towards lithium iron phosphate batteries. This is driven by their safety, weight advantages, and longer life spans. Preferences have been particularly strong among boat owners looking for efficient house batteries.

In contrast, standard flooded and gel batteries are considered more traditional choices. Some boaters value their lower upfront cost for basic applications.

Market trends also suggest a notable interest in AGM marine batteries due to their maintenance-free nature and durability.

In terms of form factors, marine dual-purpose batteries are sought after for their convenience by owners of smaller boats.

They serve both starting and power storage needs in a single unit, making them a popular choice for boaters with limited space for multiple batteries.